The goal of this application is to perform the research needed to improve cardiac mapping by examining characteristics of unipolar electrograms in order to derive information concerning the direction of wavefront propagation from individual waveforms and by using this knowledge to produce more informative maps. Mapping the spread of electrical activity in the heart with endocardial, transmural, and epicardial electrodes has proven to be a valuable technique for determining the origin of dysrhythmias in patients requiring surgical treatment of drug- resistant tachyarrhythmias, for recording data used to correlate epicardial and body surface potentials by both the forward and inverse methods, and for studying the mechanisms responsible for the spread of excitation and recovery in the normal and diseased heart. Isochronous maps, the most widely used format in cardiac mapping, imply that activation proceeds along planar surfaces when propagation is actually three-dimensional except for short distances along the epicardial and endocardial surfaces. This type of two-dimensional representation of the spread of activation may be reasonable for the endocardium due to rapid propagation throughout the Purkinje network. Since most epicardial tissue is activated transmurally from the endocardium rather than from the spread of wavefronts across the epicardium, the direction of wavefront propagation cannot be accurately define or displayed with current isochronous mapping techniques. Most of the information in each of the many electrograms used to generate an isochronous map is discarded when the activation time is extracted even though waveform shape propagation characteristics are closely related. The first specific aim is to develop a method for determining propagation information from unipolar electrograms recorded from normal and ischemic tissue. The right ventricular isolation procedure will be used to produce a data base of electrograms from normal tissue for which the relationship between fiber orientation and the initiation, propagation, and termination of wavefronts is clearly defined. This data base will be used to train and test algorithms for deriving propagation direction from unipolar electrograms. The algorithms will be tested on epicardial and endocardial electrograms containing measurable amounts of distant activity. Final testing of the algorithms will be done on electrograms recorded from normal and ischemic tissue in the left ventricle. The second specific aim is to incorporate directional information in the generation of cardiac maps which more accurately represent the spread of electrical activity in the heart.